1. Field of the Invention
The present invention relates to glass fabrics coated with protective layers that provide excellent weatherability, flexibility, moisture-resistance and electromagnetic microwave transmissibility.
2. Description of the Prior Art
The use of microwave antennas, particularly dish antennas, for transmitting and receiving microwave signals from satellites or terrestrial microwave antenna has rapidly been increased. Such dish antennas vary widely in size, but many have diameters of 1 to 7 meters. These antennas are typically placed in a location significantly elevated and remote from the surrounding structures and terrain to prevent reflection of the transmitted electromagnetic waves and to obtain a wide distance coverage. Such elevated locations are typically exposed to harsh weather conditions, such as high winds and extreme temperatures. Consequently, it is desirable that the antenna be equipped with a cover to protect the antenna assembly from the effects of weather, abrasion and photodegradation in order to ensure a reasonably durable service life of the antenna. Additionally, an antenna should be equipped with a protective cover to prevent accumulation of water or ice and uneven exposure to direct sunlight that may alter the electrical characteristics of the antenna and result in degraded antenna performance.
The selection of the cover-material is complicated by various demands imposed on the material. The cover material, for example, must not interfere with the transmissibility of electromagnetic microwaves, must be resistant to photodegradations, particularly to ultraviolet light, must have a very low moisture-absorption property, must have physical integrity to withstand harsh natural elements such as high winds and extreme temperatures, and sufficient flexibility to absorb the impacts of high winds, and falling rain and hail.
In the past, ceramic-type materials were utilized to fabricate antenna covers, but the use of ceramic covers was not satisfactory in that ceramic covers add significant weight to the antenna assembly, are susceptible to cracking, and are not readily adaptable to the varying geometry of antenna configurations. Consequently, polymer coated glass fabrics, particularly fluoropolymer coated fabrics, have been gaining wide acceptance in the antenna industry. Such a use of fluoropolymer coated glass fabric is disclosed, for example, in U.S. Pat. No. 3,896,450 to Fitzroy et al.
Glass fabrics coated with a talc and titanium mixture filled fluoropolymer that may be utilized for antenna cover applications are known in the art. Such fluoropolymer coated glass fabrics are disclosed, for example, in U.S. Pat. Nos. 4,645,709 to Klare; 4,610,918 to Effenberger et al.; and 4,770,927 to Effenberger et al.
However, it is desirable to provide a covering material for microwave antennas that has improved weatherability, flexibility, ultraviolet light-stability and physical strength as well as microwave transmissibility over the prior art fluoropolymer coated glass fabrics. Additionally, it is desirable to provide such an improved fluoropolymer coated glass fabric that is uniformly and completely coated with moisture resistant layers to prevent moisture degradation of the glass fabric.